Hughes Autoformer and Incoming Amperage question

[Mr. Goodwrench]

I store my trailer at my daughters house and several years ago I put in a 30 amp circuit and pedestal to plug into when it is in storage there. Sometimes we have guests stay in the trailer while visiting. Because of the length of run using 10 gauge wire, my voltage at the pedestal is only about 113 volts. This is adequate for normal uses but we never run the AC or microwave when we stay in the trailer at my daughters house.

In a couple of weeks, we will have some guests staying with us who are from Arizona (we live in Oregon). Now, we know that if we get any kind of hot weather, the company will want to use the AC and I don't want to ruin the unit because of low voltage. Therefore, I am considering buying a Hughes Autoformer to boost the voltage to a safe level in the trailer.

My question is what will the use of the Autoformer do to my incoming amperage from the sub panel to the pedestal? Asking around, everyone assumes that the autoformer is always used in an RV park so no worries. But this is a private residence and I don't want to overload my installation and trip the breaker in the sub panel. Can anyone give me the answer as to what an autoformer will do to the incoming amps? I know that replacing the 10 gauge wire with something heaver would be the ideal solution but having an autoformer would be useful to have while traveling too.

[kevinpo]

Hi John,
I would run the AC and test the voltage drop first and see if you really need the Hughes. Much cheaper and easy to do.

Regards,
Kevin

[jkwilson]

113V with nothing connected or with a load on it? If it’s 113 with nothing connected, it isn’t a wire size issue, but a supply issue. If so check an outlet in the house. The utility can connect a different tap on the transformer to bring line voltage to the proper level.

[Mr. Goodwrench]

As a test, I have run the AC and it pulls the incoming voltage down to about 108 volts. When running, the AC doesn't sound right and I am afraid it will burn out. Therefore, I am considering the Hughes Autoformer but I can't find out what this will do to my incoming circuits amperage and whether it will trip the breaker.

[kevinpo]

John,
You are correct that is too low voltage. As JKWilson said voltage should be higher than 113 unless it's low at the source. The AC shouldn't pull more than about 16A at startup so you should be good for that with the Hughes.

Regards,
Kevin

[jkwilson]

As a test, I have run the AC and it pulls the incoming voltage down to about 108 volts. When running, the AC doesn't sound right and I am afraid it will burn out. Therefore, I am considering the Hughes Autoformer but I can't find out what this will do to my incoming circuits amperage and whether it will trip the breaker.

If 113 is the voltage with no load, you are seeing about 4.5% drop. You wouldn’t plan on that much, but it probably won’t be a problem. If 113 is no load, there is a utility problem that you should address first.

[Mr. Goodwrench]

113 volts is no load at the trailer. 118 volts no load at the sub panel feeding trailer. 108 volts at trailer with AC running. I don't know running amps at the sub panel yet but will check it out.

[Mr. Goodwrench]

While trying to find an answer to my question about what happens to the incoming amperage, I ran across this statement made by David Zomorrodian, one of the owners of Hughes Autoformers: "The autoformer changes amps into volts and draws fewer amps from the park and converts those amps into more volts inside the RV."

Now, somehow to my thinking and limited knowledge of electrical theory, this seems to be some snake oil marketing and bordering on the absurd! Would anyone who knows electrical theory care to jump in here?

[jkwilson]

113 volts is no load at the trailer. 118 volts no load at the sub panel feeding trailer. 108 volts at trailer with AC running. I don't know running amps at the sub panel yet but will check it out.

If there is no load, you will see the same voltage at both ends of the wire. Even with undersized wire and bad connections.

[jkwilson]

While trying to find an answer to my question about what happens to the incoming amperage, I ran across this statement made by David Zomorrodian, one of the owners of Hughes Autoformers: "The autoformer changes amps into volts and draws fewer amps from the park and converts those amps into more volts inside the RV."

Now, somehow to my thinking and limited knowledge of electrical theory, this seems to be some snake oil marketing and bordering on the absurd! Would anyone who knows electrical theory care to jump in here?

Brief electrical theory. A transformer couples AC voltage by using two coils right next to each other. When current flows in one, current is induced in the other. If both sides have the same number of loops, the output voltage is the same as the input voltage. If the output coil has more loops than the input coil, the output voltage will be higher than the input voltage. If the input coil has more loops, the output voltage will be lower than the input. Input power and output power stay about the same minus some inefficiency.

An RV autoformer works by measuring input voltage. If it is acceptable, the autoformer selects the 1:1 coil and the output voltage is whatever you feed it. If the autoformer sees low voltage, it switches to a 1:1.1 coil and boosts the output voltage.

Some things, like AC motors are less efficient as voltage drops, so you can end up drawing less current with the autoformer boosting the voltage. Otherwise it’s close to a wash. Many people say an autoformer uses more power because in a campground it lets you keep running everything so you are kind of using more power because you can still operate everything when others have to shut down because of low voltage.